Ultrafine particles and method and apparatus for producing the same

ABSTRACT

The present invention provides a method of producing ultrafine particles by vaporization comprising: vaporizing a target by sputtering; causing particles that fly from the target by vaporization to be deposited on an oil surface; and recovering the oil on which the flown particles have deposited to obtain individually dispersed ultrafine particles.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to ultrafine particles, and to amethod and an apparatus for producing the same. As used herein, the term“ultrafine particle” refers to fine particles having an average particlesize ranging from 1 nm to 50 nm, that is, so-called “nano sizeparticles” (occasionally referred to as “nano particles”).

[0003] 2. Description of the Related Art

[0004] Conventionally, various methods of producing ultrafine particleshave been researched. Since nano particles having an average particlesize of below dozens of nano meters cannot be obtained by grinding,build-up methods have been used. Primary examples of build-up methodscan be divided into gas phase methods, such as condensation byevaporation and vapor phase reaction, and liquid phase methods, such asprecipitation and desolvation.

[0005] As an example of a liquid phase method, Japanese PatentApplication Laid-Open (JP-A) No. 2000-54012 discloses a method offorming, through reduction, magnetic nano crystals made of metals,intermetallic compounds and alloys. Although it is possible to obtainultrafine particles having a relatively uniform particle size, themethod has limitations in that raw materials must be dissolved as asolution and only a compound having a stoichiometric composition ratiois obtained.

[0006] When the gas phase method is used, a thin film can relativelyeasily be formed. However, various procedures are needed to recover aproduct in the form of nano particles. For example, JP-A No. 2001-35255introduces silver or oxygen using in-gas evaporation to obtain nanoparticles of silver oxide. The Journal of Crystal Growth 45 (1978), pp.490 to 494, proposes a method of producing ultrafine particles of higherpurity by vacuum evaporation on a rheological oil surface (VEROSmethod). In this method, resistance overheating or an electron beam isused as the evaporation source. However, although these methods aresuitable for forming particles made of a single-element of noble metals,it is difficult to produce ultrafine particles made of two or more metalelements. It is also the case that there is no effective way ofproducing nano particles of alloys having an arbitrary composition.

[0007] In the VEROS method described above, resistance overheating, anelectron beam or the like is used for vaporization. In this method, whena multi-element base target is used, a problem arises in that, timing ofevaporation may shift depending on a difference in a vapor pressure,whereby only giving single-element particles and failing to producecomposite particles. In order to solve this problem, it is conceivableto use ion beams as vaporizing means to vaporize a multi-element basetarget having the form of molecules or an alloy. However, in this case,vaporization efficiency is poor and the apparatus cost is high. Further,these methods require a relatively high vacuum. In order to individuallydisperse fine particles, it is necessary to either discharge thevaporized molecules from the system before aggregation occurs or protectthe surface, and for this purpose, a medium that adheres to the surfacesof particles must be present in the vacuum system. Consequently, thereare problems in that the degree of vacuum is decreased and thevaporizing means cannot function in an ordinary manner.

[0008] As stated above, it is difficult to obtain nano size particleshaving a variety of compositions and applicable to various objects byliquid phase methods, and such nano size particles cannot be obtained bygas phase methods such as a CVD method. Because particles aggregate toform a film within one to several seconds even if ordinary sputtering isused, there is currently no specific method capable of producing nanosize particles.

[0009] Moreover, when arranging nano particles in the form of a film, itis effective to coat a colloidal solution of nano particles. However, itis necessary to select a dispersing medium and a coating equipmentsuited for particle constituent elements. Although gas phase methods areknown in which fine particles are recovered by causing vaporizedparticles to adhered to a dispersion medium, there is the problem thatthe particles easily coagulate when their concentration is high. Therehas also been a demand for a method of readily producing a stablecolloidal solution of nano particles.

SUMMARY OF THE INVENTION

[0010] An object of the present invention is to solve the aforementionedproblems associated with the prior art and to attain the followingobject. That is, an object of the invention is to provide a method andan apparatus for readily producing individually dispersed ultrafineparticles having an arbitrary composition and an arbitrary compositionratio and a colloidal solution thereof at a low cost, and to provideultrafine particles that are obtained by the method and the apparatus.

[0011] The aforementioned problems are solved by the following means.

[0012] A first aspect of the invention is a method of producingultrafine particles by vaporization comprising: vaporizing a target bysputtering; causing particles that fly from the target by vaporizationto be deposited on an oil surface; and recovering the oil on which theflown particles have deposited to obtain individually dispersedultrafine particles.

[0013] A second aspect of the invention is a method of producingultrafine particles by vaporization comprising: vaporizing a target bysputtering; cooling and solidifying particles that fly from the targetby vaporization; and recovering the flown particles that have beensolidified by cooling to obtain individually dispersed ultrafineparticles.

[0014] A third aspect of the invention is an apparatus for producingultrafine particles by vaporization comprising: means for vaporizing atarget by sputtering; an oil on which particles that fly from the targetby vaporization are deposited; and means for recovering the oil on whichthe flown particles have deposited.

[0015] A fourth aspect of the invention is an apparatus for producingultrafine particles by vaporization comprising: means for vaporizing atarget by sputtering; means for cooling and solidifying particles thatfly from the target by vaporization; and means for recovering the flownparticles that have been solidified by cooling.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a schematic structural view showing a first embodimentof an apparatus for producing ultrafine particles of the presentinvention.

[0017]FIG. 2 is a schematic structural view showing a second embodimentof an apparatus for producing ultrafine particles of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] First and second embodiments of the present invention aredescribed in detail below. An apparatus for producing ultrafineparticles of the invention, the ultrafine particles of the invention,and a method of producing the ultrafine particles of the invention arealso described.

[0019] First Embodiment

[0020] The method according to the first embodiment of the invention isa method of producing ultrafine particles by vaporization comprising:vaporizing a target by sputtering; causing particles that fly from thetarget by vaporization to be deposited on an oil surface; and recoveringthe oil on which the flown particles have deposited to obtainindividually dispersed ultrafine particles.

[0021] In the method of producing ultrafine particles according to thefirst embodiment of the invention, multi-element based ultrafineparticles can be produced by employing sputtering for vaporization(vaporizing means). Further, particles can be flown normally in thepresence of a medium such as an oil even under vacuum. By causingparticles to be deposited on an oil surface, individually dispersedultrafine particles can readily be obtained without causing aggregationof the particles. Therefore, by the method of producing ultrafineparticles according to the first embodiment, individually dispersedultrafine particles having an arbitrary composition and an arbitrarycomposition ratio or a colloidal solution thereof can stably beobtained, in a simple manner and at a low cost.

[0022] In the method of producing ultrafine particles according to thefirst embodiment of the invention, suitable examples of the oil to forman oil surface include silicone-based oils having a boiling point of200° C. or more, α-terpineol, hydrocarbons having 6 or more carbon atomsand alcohols having a high boiling point. Various additives may beincluded in these oils. Preferable examples of the additive includealkylphosphine oxides, alkylphosphines and the compounds containing atleast one selected from —SH, —CN, —NH₂, —SO₂OH, —SOOH, —OPO(OH)₂ and—COOH. Among them, alkylphosphine oxides and the compounds containing atleast one selected from —SH and —COOH are preferable. It is appropriatethat the oil has been deaerated.

[0023] In the method of producing ultrafine particles according to thefirst embodiment of the invention, it is preferable that the oil surfaceis formed on a substrate (a flat plate) such that a suitable oil thinfilm can readily be formed. The substrates are preferably made of metalsor resins which have been smooth-treated. The substrates are selectedfrom the materials that are adaptable to the oil used. It isparticularly preferable if an oil thin film is formed uniformly on asubstrate and can be fluidized at an arbitrary speed as described later.Therefore, for the purpose of controlling the surface tension of thesubstrate, it is preferable to perform surface treatment of thesubstrate as necessary.

[0024] In the method of producing ultrafine particles according to thefirst embodiment of the invention, it is preferable that the oil surfaceis a fluidized oil surface obtained by fluidizing an oil, from thestandpoints of recovering an oil efficiently and obtaining individuallywell-dispersed ultrafine particles. By causing particles to be depositedon the fluidized oil surface, particle growth can be suppressed, wherebyultrafine particles having a minute and uniform particle size canreadily be obtained. As the method of fluidizing an oil, i.e., themethod of forming a fluidized surface, the method to form the fluidizedsurface on a rotating substrate surface, the method to form thefluidized surface on an inclined substrate, and the like are suitablyused. These methods may be used in combination. As used herein, the term“inclined” of the inclined substrate means that a vertical line on thesubstrate surface is inclined with respect to the gravity direction.

[0025] In case of forming a fluidized surface on the surface of arotating substrate, when a substrate processed to have the shape of adisk is rotated, an oil can uniformly be fluidized to achieve apreferable fluidized oil surface in a simple manner. The rotationalspeed of the rotating substrate preferably ranges from about 10 rpm toabout 500 rpm. An oil is preferably supplied from a positionsubstantially around the center of the rotating shaft of the rotatingsubstrate, and the supply is continuously maintained withoutinterruption. The oil feeding speed is preferably from 0.01 ml/min to 2ml/min per unit area of the rotating substrate. The fluidized oilsurface may be formed either at the upper surface (the surface providedopposite to the gravity direction: in this case sputtering is conductedin the direction of downward) or at the lower surface (the surfaceprovided in the gravity direction: in this case sputtering is conductedin the direction of upward) of the rotating substrate. It is morepreferable to form a fluidized surface on the upper surface of therotating substrate. If a fluidized oil surface is formed at the lowersurface of the rotating substrate, there may arise a problem that an oildrops on a vaporizing means to cause pollution or other troublesdepending on a low rotational speed and physical properties of an oil(e.g., low viscosity). Besides, if conducted downwardly, sputtering canrelease flown particles more efficiently. From the standpoints, it ispreferable to form a fluidized oil surface on the upper surface of therotating substrate.

[0026] In case of forming a fluidized oil surface on an inclinedsubstrate surface, it is suitable that oil supply is carried out suchthat an oil can spread over an entire surface of the inclined substrate.For example, it is preferable to supply an oil such that the oil canflow from the upper end to the lower end of the inclined substrate.

[0027] Suitably, a substrate is cooled in both of the rotating substratemethod and the inclined substrate method described above. A substratemay be cooled in the same manner as conducted by a cooling method(means) described in the second embodiment below. Water may be used as acooling medium.

[0028] In the method of producing ultrafine particles according to thefirst embodiment of the invention, when the above-described rotatingsubstrate method is employed, an oil on which flown particles (ultrafineparticles) have deposited can be recovered, for example, in such amanner that particles that collided (deposited) to the fluidized oilsurface of the rotating substrate surface are flown to the periphery bya centrifugal force caused by rotation of the rotating substrate, andthe oil flown outside of the periphery and including the particles iscaptured by a member which protects the substrate periphery and then theoil is collected to one site. In the inclined substrate method, an oilthat has dropped on the lower end of the inclined substrate may bestored in a tank and the like. In both of the above-described rotatingsubstrate method and inclined substrate method, an oil may be suppliedin a circulating mode. That is, the oil recovered at an oil recoveringportion can be delivered, for circulation, to an oil feeding portionsuch that the oil can be continuously used until ultrafine particles(flown particles) reach a predetermined concentration.

[0029] The recovered oil may be concentrated by vacuum or vacuumheating, as necessary. Further, after recovered, the oil may preferablybe replaced with other organic solvents (e.g., organic solvents having alower boiling point than that of the oil, such as, toluene, xylene,hexane, alcohols having 6 or less carbon atoms) depending on usepurposes. The concentration rate may vary and range from about 10 to 40%by weight, depending on the composition of ultrafine particles and thesolvent used.

[0030] The first embodiment of an apparatus suitably used for the methodof producing ultrafine particles according to the invention isillustrated below, referring to a drawing.

[0031] The apparatus for producing ultrafine particles shown in FIG. 1comprises a sputtering device 12 for vaporization (vaporizing means) anda rotating substrate 14 capable of rotating to form a fluidized oilsurface in a vacuum chamber 10. The sputtering device 12 has, forexample, a target (not shown) having a necessary composition previouslyprepared by calcination, and additionally, a shutter 16 in the vacuumchamber 10. The rotating substrate 14 has a vacant structure to which acooling medium is introduced from a cooling medium inlet 18, to cool therotating substrate 14 from inside. Regions around the periphery of therotating substrate 14 are covered with a protecting member 20. To serveas the particle recovering means, the protecting member 20 is connectedwith an oil recovering tube 22 in the shape of a float, and the oilrecovering tube 22 is further connected with an oil recovering tank 24outside of the vacuum chamber 10. In the vicinity of the rotating shaftof the rotating substrate 14, an oil feeding tube 26 is arranged toenable an oil supplied to the upper surface near the rotating shaft ofthe rotating substrate 14. The oil feeding tube 26 is connected with anoil feeding tank 28 outside of the vacuum chamber 10. And to the oilfeeding tank 28, an evacuating tube 30 is connected. Rotation of therotating substrate 14 is controlled by a motor 32.

[0032] In an apparatus for producing ultrafine particles shown in FIG.1, a cooling medium is introduced from the cooling medium inlet 18 tocool the rotating substrate 14. Rotation of the rotating substrate 14 iscontrolled by the motor 32, and an oil is continuously supplied, throughthe oil feeding tube 26, to a position around the rotating shaft of therotating substrate 14 from the oil feeding tank 28, to thereby form afluidized oil surface. In this operation, an oil has previously beendeaerated through an evacuating tube 30. The shutter 16 provided for thesputtering device 12 is opened to expose a target (not shown) to thevacuum chamber 10 to initiate sputtering. In the initial period, theoxides present on the surface of the target are eliminated and thensputtering is commenced. The flown particles reach the fluidized oilsurface formed on the upper surface of the rotating substrate 14, flyaway to the periphery by a centrifugal force together with a fluidizedoil, are captured by the protecting member 20, and then are collected tothe oil recovering tank 24 through the oil recovering tube 22. Thus,ultrafine particles can be obtained. The recovered oil containing theflown particles (ultrafine particles) may be concentrated and replaced,as necessary, to give a desired colloidal product.

[0033] Second Embodiment

[0034] The method according to the second embodiment of the invention isa method of producing ultrafine particles by vaporization comprising:vaporizing a target by sputtering; cooling and solidifying particlesthat fly from the target by vaporization; and recovering the flownparticles that have been solidified by cooling to obtain individuallydispersed ultrafine particles.

[0035] In the method of producing ultrafine particles according to thesecond embodiment of the invention, multi-element based ultrafineparticles can be produced by employing sputtering for vaporization(vaporizing means). Further, particles can be flown normally in thepresence of a medium such as a vaporized medium even under vacuum. Bycooling and solidifying the flown particles, individually dispersedultrafine particles can readily be recovered without causing aggregationof the particles. Therefore, by the method of producing ultrafineparticles according to the second embodiment, individually dispersedultrafine particles having an arbitrary composition and an arbitrarycomposition ratio or a colloidal solution thereof can stably beobtained, in a simple manner and at a low cost.

[0036] In the method of producing ultrafine particles according to thesecond embodiment of the invention, in order to perform cooling andsolidifying (cooling and solidifying means), for example, a substrate iscooled (a cooled substrate is provided) and the particles flown bysputtering are frozen on the surface of the cooled substrate. In orderto cool the substrate, a cooling medium such as liquid nitrogen, liquidcarbon dioxide and super-cooled water may be used. By cooling thesubstrate in such a manner, the flown particles (ultrafine particles)are cooled and solidified (frozen) to cause deposition thereof on thesurface of the substrate. Preferably, cooling of the substrate isconducted, for example, by inside cooling in which a cooling medium iscirculated into the substrate in order to efficiently deposit the flownparticles on the surface of the substrate. The substrate may be rotatedat a relatively low speed.

[0037] In the method of producing ultrafine particles according to thesecond embodiment of the invention, it is preferable to use and mediatea vaporized medium. That is, when the substrate is cooled forsolidifying the particles, a vaporized medium is adsorbed to the surfaceof the flown particles (cooling and solidifying means) for modifying thesurface, and then the flown particles are cooled and solidified. For useas the vaporized medium, solvents having a relatively low boiling pointare preferable. For example, organic solvents having a boiling point of200° C. or lower are preferable, and more preferable are the organicsolvents having a boiling point of 150° C. or lower. Alcohols areparticularly preferable. Cooling of the flown particles is acceleratedby contacting the particles with a vaporized solvent. Since thevaporized solvent is adsorbed to the surface of the particles formodification thereof, the flown particles are frozen and deposited onthe surface of the substrate together with the vaporized solvent. Theflown particles (ultrafine particles) are prevented from aggregatingwith additional particles that will be flown later, by an effect of thevaporized solvent adsorbed to the particle surface, to thus produceultrafine particles having a small particle size and a narrower particlesize distribution. It is also preferable to use, together with thevaporized medium, an adsorbent having a different adsorbing force to thesurface of flown particles such that the adsorbent can contact with theflown particles. Suitable examples of the adsorbent includealkylphosphine oxides, alkylphosphines and the compounds containing atleast one selected from —SH, —CN, —NH₂, —SO₂OH, —SOOH, —OPO(OH)₂ and—COOH. Among them, alkylphosphine oxides and the compounds containing atleast one selected from —SH and —COOH are preferable. More specifically,as a lipophilic adsorbent, adsorbing compounds containing a substituenthaving a total of 6 or more carbon atoms, preferably 8 to 40 carbonatoms, such as an octyl group, a decyl group, a dodecyl group and ahexadecyl group can be used. As a hydrophilic adsorbing agent, adsorbingcompounds having a substituent or a hydrophilic group having 6 or lesscarbon atoms (e.g., —SO₃M, —COOM in which M represents a hydrogen atom,an alkali metal atom, an ammonium molecule and the like) can suitably beused. The fact that the surface of the flown particles (ultrafineparticles) is adsorbed by a vaporized medium or an adsorbent can beconfirmed by high resolution TME, such as FE-TEM to find that aspecified distance is left between the particles, or by chemicalanalysis.

[0038] In the method of producing ultrafine particles according to thesecond embodiment of the invention, the flown particles (ultrafineparticles) solidified by cooling (frozen) can be recovered, for example,by the following procedure. When a substrate is cooled by liquidnitrogen and the like, the flown particles are frozen and deposited onthe substrate surface, after which sputtering and the liquid nitrogensupply are halted, vacuum is leaked, the substrate is rotated withgradually raising the temperature to cause the deposited particles(ultrafine particles) adhered by the vaporized solvent to be molten andflown away to the periphery by a centrifugal force, then to be capturedby a protecting member arranged around the periphery of the substrate,and finally to be collected to one site.

[0039] The second embodiment of an apparatus suitably used for themethod for producing ultrafine particles according to the invention isillustrated below, referring to FIG. 2. Members having the samefunctions as those in an apparatus shown in FIG. 1 are designated by thesame symbols.

[0040] The apparatus for producing ultrafine particles shown in FIG. 2comprises a sputtering device 12 for vaporization (vaporizing means) anda rotating substrate (a cooled substrate) 14 capable of rotating and ofcooling and solidifying the flown particles in a vacuum chamber 10, andadditionally, a vaporized medium inlet 34 to introduce a vaporizedmedium into the vacuum chamber 10. The sputtering device 12 has, forexample, a target (not shown) having a necessary composition previouslyprepared by calcination, and additionally, a shutter 16 in the vacuumchamber 10. The rotating substrate 14 has a vacant structure to which acooling medium is introduced from a cooling medium inlet 18, to cool therotating substrate 14 from inside. Regions around the periphery of therotating substrate 14 are covered with a protecting member 20. To serveas the particle recovering means, the protecting member 20 is connectedwith a recovering tube 22 in the shape of a float, and the recoveringtube 22 is further connected with a recovering tank 24 outside of thevacuum chamber 10. Rotation of the rotating substrate 14 is controlledby a motor 32.

[0041] In an apparatus for producing ultrafine particles shown in FIG.2, a cooling medium is introduced from the cooling medium inlet 18 tocool the rotating substrate 14. A vaporized medium is introduced intothe vacuum chamber 10 from a vaporized medium inlet 34. The rotatingsubstrate 14 is rotated by a motor at a low speed of, for example, about10 to 30 rpm. The shutter 16 provided for the sputtering device 12 isopened to expose a target (not shown) to the vacuum chamber 10 toinitiate sputtering. In the initial period, the oxides present on thesurface of the target are eliminated and then sputtering is commenced.The particles flown by sputtering are brought into contact with avaporized medium to cause surface modification or surface adsorption bythe vaporized medium, and then are frozen and deposited on the uppersurface of the cooled rotating substrate 14. Thereafter, introduction ofthe cooling medium from the cooling medium inlet 18 is halted. At thetime when the frozen and deposited substance starts melting, therotational speed of the rotating substrate 14 is increased. The frozendeposit is molten and then flown away to the periphery by a centrifugalforce caused by rotation of the rotating substrate 14, and is capturedby a protecting member 20, and thereafter is collected to a collectingtank 24 via a collecting tube 22. Thus, ultrafine particles can beobtained. Further, the flown particles (ultrafine particles)—containingmolten deposit recovered can be concentrated and then replaced, asnecessary, to give a desired colloidal product.

[0042] The procedures which are common to the first and secondembodiments of the invention are described below.

[0043] In the method of producing ultrafine particles of the invention,sputtering can be conducted by conventionally known methods. Sputteringmay be conducted without any restriction, in the direction of upwardly,downwardly and in the left and right directions. In the invention,“downward” means the gravity direction, and “upward” means the oppositedirection.

[0044] In the method of producing ultrafine particles of the invention,the target may be any of single-element compounds and multi-elementcompounds of two or more elements. According to the present invention,it is possible to produce preferable ultrafine particles made ofmulti-element compounds consisting of two or more elements.Specifically, various composite materials can be used, not to mention ofordinarily used metals, intermetallic compounds or sulfides, and siliconand the oxides thereof. Further, when silver, gold, copper, zinc, iron,cobalt, chromium, nickel, aluminum, as well as chalcogen compounds suchas indium, antimony, tellurium and the composite compounds thereof areused, an advantageous effect of the present invention can be exhibited.As the multi-element compound, the oxides and sulfides containing atleast one of the metals in the 4th to the 6th periods in the periodictable or the oxides and sulfides of a multi-metal consisting of two ormore metals are preferable, and multi-element compounds containing theelements of the groups III, IV, V and VI in the 4th to the 6th periodsin the periodic table (at least one element selected from the groups of13, 14, 15 and 16 according to IUPAC, 1989, inorganic chemicalnomenclature, revised version) are more preferable. More specifically,the oxides and sulfides of magnesium, aluminum, silicon, titanium,vanadium, manganese, copper, zinc, gallium, strontium, yttrium,zirconium, silver, indium, cesium, barium and the like, or the oxidesand sulfides of the composite material thereof, or multi-elementcompounds containing silver, germanium, indium, antimony, tellurium andthe like in an arbitrary composition ratio are preferable. In theinvention, ultrafine particles made of metal multi-element compoundshaving a stoichiometrically non-applicable composition ratio can readilybe produced.

[0045] It is preferable in the invention that the distance between atarget and an oil surface (or a substrate surface for deposition) canarbitrarily be varied. By varying the distance, particle sizes andsurface modification levels may be controlled, whereby applicability ofthe ultrafine particles can be enlarged.

[0046] In the method of the invention, it is possible to produceultrafine particles having an arbitrary composition and an arbitrarycomposition ratio, so long as sputtering can be implemented for a givencomposition. Therefore, ultrafine particles obtained by the method ofthe invention (ultrafine particles of the invention) can be applied andused in various fields. For example, in optical recording materials,metal chalcogen compounds are used as the recording material. If themetal chalcogen compounds are used in the form of ultrafine particlesproduced by the present invention, recording sensitivity and recordingdensity can be improved. A functional film can also be obtained by usingthe ultrafine particles of the invention. A metal chalcogen compoundused for optically recording has a composition of Ag, In, Sb and Te, orGe, Sb and Te, each included in non-stoichiometric ratio. Therefore, itis difficult to formulate the components into a single particle bysynthesis. However, ultrafine particles can be produced by the method ofthe present invention if the calcinated metal chalcogen compound is usedas a target for sputtering.

[0047] The ultrafine particles obtained by the invention may be includedin a layer used for a dielectric material layer which is a constituentelement of the optical recording material (particularly, DVD disk).Besides, the ultrafine particles of the invention may be used in afunctional layer, in addition to a recording layer and a dielectricmaterial layer.

[0048] Furthermore, the obtained ultrafine particles of the inventionmay be used in the form of a colloidal solution in an organic solvent.Alternatively, a hydrophilic solvent may be replaced to produce ahydrophilic colloidal solution. These colloidal solutions can bespin-coated or web-coated, to give a thinner film.

EXAMPLES

[0049] The present invention is described further in detail below withreference to the following examples, but it is to be understood that theinvention is not limited to the examples.

Example 1

[0050] Ultrafine particles (nano particles) were produced as follows byusing an apparatus shown in FIG. 1. In order to produce a target forsputtering, metals of Ag, In, Sb and Te were calcinated at a weightratio of 1:1:18:7 and the produced target was placed in the sputteringapparatus 12 using a 4-inch backing plate. As the rotating substrate 14,a vacant substrate in the form of disc having a diameter of about 30 cmwas produced and rotated at a rotational speed of 450 rpm using themotor 32 while water-cooling was provided by introducing cooling waterfrom the cooling medium inlet 18. α-Terpineol was deaerated for use asan oil, and then supplied through the oil feeding tube 26 to the uppersurface of the rotating substrate 14 at a feeding speed of 30 ml/min. Inthe sputtering device 12, an RF high-rate electric source and a 4-inchplanar magnetron-type cathode were used. Inside the vacuum chamber 10, adiffusion pump and a rotary pump were arranged to control the degree ofvacuum for sputtering.

[0051] Ten minutes after the particle production started, an interval of3 minutes was provided, and this procedure was repeated three times, tothus perform sputtering for a total of 30 minutes. The particlesdispersed in about 700 ml of the recovered oil were observed by atransmission-type electron microscope TEM, to find that nano particleshad an average particle size ranging from 3 to 8 nm.

[0052] The composition of one particle was investigated by using EF-TEM,to reveal the presence of four elements Ag, In, Sb and Te.

Example 2

[0053] Ultrafine particles (nano particles) were produced as follows byusing an apparatus shown in FIG. 2. In order to produce a target forsputtering, metals of Ag, In, Sb and Te were calcinated at a weightratio of 1:1:18:7 and the produced target was placed in the sputteringapparatus 12 using a 4-inch backing plate. As the rotating substrate 14,a vacant substrate in the form of disc having a diameter of about 30 cmwas produced and rotated at a rotational speed of 450 rpm using themotor 32 while water-cooling was provided by introducing cooling waterfrom the cooling medium inlet 18. 1-ethoxy-2-propanol containing about0.1% of sodium mercaptosuccinate and having been vaporized to a degreecapable of sputtering was introduced from the vaporized medium inlet 34into the vacuum chamber. In the sputtering device 12, an RF high-rateelectric source and a 4-inch planar magnetron-type cathode were used.Inside the vacuum chamber 10, a diffusion pump and a rotary pump werearranged to control the degree of vacuum for sputtering.

[0054] Five minutes after the particle production started, an intervalof 1 minute was provided, and this procedure was repeated five times, tothus perform sputtering for a total of 25 minutes. Thereafter, Ar wasintroduced into the vacuum chamber 10 to raise the pressure to a normalpressure, and the liquid nitrogen supply was halted. When the frozendeposit on the rotating substrate 14 started melting, a rotational speedof the rotating substrate 14 was increased to 250 rpm, and the moltendeposit was recovered.

[0055] The particles present in a dispersion (molten deposit) wereobserved by a transmission-type electron microscope TEM, to confirm thatnano particles having an average particle size ranging from 3 to 8 nmcould be produced, as obtained in Example 1. This dispersion did notcause precipitation and excellent colloidal conditions were maintainedeven after 7 hours at an ordinary temperature.

[0056] The composition of one particle was investigated by using EF-TEM,to reveal the presence of four elements Ag, In, Sb and Te.

Example 3

[0057] Ultrafine particles (nano particles) were produced in a similarmanner as in Example 2 except that in place of sodium mercaptosuccinate,polyvinylpyrrolidone having a molecular weight of 1600, sodium citrateand a hydrolyzate of tetraethoxy orthosilicate (TEOS) were used,respectively. The obtained multi-element base nano particles maintainedexcellent dispersibility.

Example 4

[0058] Ultrafine particles (nano particles) were produced in a similarmanner to Example 1 except that a calcinated metal made of Ge, Sb and Teat a weight ratio of 2:3:5 was used as a target for sputtering. Theresultant ultrafine particles were observed by EF-TEM, to find that thethree elements were included in a particle at approximately the sameproportion as above. The average particle size ranged from 3 to 9 nm.

[0059] As described above, the present invention can provide a methodand an apparatus for stably producing individually dispersed ultrafineparticles having an arbitrary composition and an arbitrary compositionratio or a colloidal solution thereof in a simple manner and at a lowcost, and also provide the ultrafine particles obtained by the methodand the apparatus.

What is claimed is:
 1. A method of producing ultrafine particles byvaporization comprising: vaporizing a target by sputtering; causingparticles that fly from the target by vaporization to be deposited on anoil surface; and recovering the oil on which the flown particles havedeposited to obtain individually dispersed ultrafine particles.
 2. Themethod according to claim 1, wherein the oil surface is a fluidized oilsurface prepared by fluidizing an oil.
 3. The method according to claim2, wherein the fluidized oil surface is formed on the surface of arotating substrate.
 4. The method according to claim 2, wherein thefluidized oil surface is formed on the surface of an inclined substrate.5. The method according to claim 1, wherein the target is amulti-element compound.
 6. The method according to claim 5, wherein themulti-element compound contains at least one of the metals in the 4th tothe 6th periods in the periodic table.
 7. The method according to claim5, wherein the multi-element compound contains at least one elementselected from the elements of the groups III, IV, V and VI in the 4th tothe 6th periods in the periodic table.
 8. Ultrafine particles obtainedby the method according to claim
 1. 9. A method of producing ultrafineparticles by vaporization comprising: vaporizing a target by sputtering;cooling and solidifying particles that fly from the target byvaporization; and recovering the flown particles that have beensolidified by cooling to obtain individually dispersed ultrafineparticles.
 10. The method according to claim 9, wherein the flownparticles are cooled and solidified by a cooled substrate.
 11. Themethod according to claim 9, wherein the flown particles are cooled andsolidified after a vaporized medium has been modified or adsorbed to thesurfaces of the flown particles.
 12. The method according to claim 10,wherein the flown particles are cooled and solidified after a vaporizedmedium has been modified or adsorbed to the surfaces of the flownparticles.
 13. The method according to claim 9, wherein the target is amulti-element compound.
 14. The method according to claim 13, whereinthe multi-element compound contains at least one of the metals in the4th to the 6th periods in the periodic table.
 15. The method accordingto claim 9, wherein the multi-element compound contains at least oneelement selected from the elements of the groups III, IV, V and VI inthe 4th to the 6th periods in the periodic table.
 16. Ultrafineparticles obtained by the method according to claim
 9. 17. An apparatusfor producing ultrafine particles by vaporization comprising: means forvaporizing a target by sputtering; an oil on which particles that flyfrom the target by vaporization are deposited; and means for recoveringthe oil on which the flown particles have deposited.
 18. An apparatusfor producing ultrafine particles by vaporization comprising: means forvaporizing a target by sputtering; means for cooling and solidifyingparticles that fly from the target by vaporization; and means forrecovering the flown particles that have been solidified by cooling.